The invention relates to a hybrid gas generator.
Conventional hybrid gas generators comprise a chamber that contains pressurized fluid and that is sealed off by a rupturable membrane, a pyrotechnical propellant charge that ruptures the membrane when it is ignited, and a nozzle wall that is arranged between the propellant charge and the membrane and that has at least one passage opening through which the combustion products generated upon ignition of the pyrotechnical propellant charge flow towards the membrane.
These hybrid gas generators normally operate with pressurized gas which, when it flows out, mixes with the hot combustion products of the propellant charge. The resultant mixed gas then enters a restraint means, for example, an airbag or a chamber of an actuator to actuate a vehicle occupant restraint system. The passage openings in the nozzle wall have the task of aiming the generated flow of combustion products precisely at the membrane in order to break it open. as quickly as possible. Until now, arched passage openings arranged along a circle have been arranged uniformly and at close distances from each other, so that a circular disk is separated from the membrane by the combustion products. The advantage of such an arrangement is that a very large opening is made in the membrane very quickly and, consequently, a large volume of pressure fluid can escape from the chamber very quickly. The so-called resultant freed sections of the membranes are those sections that do not remain attached to the edge of the membrane but rather that are entrained with the fluid and gas flow and that enter a downstream filter, which they partially clog. The edge of the membrane can also be formed by a ring-shaped holding ring that is connected in once piece with the membrane skin to form a prefabricated unit.
The invention offers the possibility to build a smaller and lighter hybrid gas generator that has high capacity. According to the invention, a hybrid gas generator comprises a chamber that contains pressurized fluid and that is sealed off by a rupturable membrane, and a pyrotechnical propellant charge that ruptures the membrane when it is ignited. The gas generator further comprises a nozzle wall that is arranged between the propellant charge and the membrane and that has at least one passage opening through which combustion products generated upon ignition of said pyrotechnical propellant change flow towards the membrane. The passage opening has such a shape and is oriented with respect to the membrane in such a way that, when the membrane is ruptured, there are formed sections of said membrane that remain all connected to an edge of the membrane. Whereas the state of the art purposefully endeavors to make the largest possible opening in the membrane, creating at least one freed section that is no longer connected to the edge, the invention takes a different approach. According to the invention, no such freed sections are created any more but rather, due to the special arrangement and geometry of the passage opening or several passage openings, sections of the membrane are formed that remain all connected to the edge of the membrane which anyway is permanently attached to a stationary wall inside the gas generator. Since no free segments of the membrane are formed, the filter normally provided can be designed so as to be much less powerful or, as the invention preferably proposes, it can be dispensed with entirely. Even a less powerful, wider-meshed filter saves weight and space; by dispensing with the filter, it is even possible to do entirely without filter chamber, which had been provided until now.
Due to the arrangement and geometry of the passage opening, preferably a center section is separated from the membrane, which remains connected to the edge of the membrane via a bridge or a web (an area not subjected to the blast of combustion products). The center section then swings towards the outside when it is opened, without being entrained by the fluid flow or by the flow of combustion products.
Preferably several arched or ring-segment-shaped passage openings are provided which are adjacent to each other in the circumferential direction, at least two of which are at such a large distance from each other that a center section separated from the membrane remains connected to the edge of the membrane via a web.
The web is preferably formed in that, relative to the center of the membrane, there is no passage opening in an area enclosing an angle from 80xc2x0 to 120xc2x0. Consequently, in this area, no combustion products flow directly against the membrane, which remains intact in this section.
Another embodiment provides for the passage opening to be star-shaped. Due to the star-shaped design, the membrane is first opened in the center and then tears open radially toward the outside, which allows a fast opening procedure.
Preferably, the radial sections have a decreasing width towards their radially outer ends. As a result, a larger quantity of the combustion products will strike the membrane in the area of the center of the star and lead to a fast opening there. A delay of the opening procedure towards the edge is not to be expected, in spite of the decreasing width of the radial sections, since the pressure of the fluid additionally enhances the tearing open of the membrane as soon as it has been opened in the center.
According to the preferred embodiment, a total of three radial sections is provided, which are at a uniform distance from each other along the circumference. Since only three sections form the passage opening, relatively large sections of the membrane are formed, which remain attached to the edge over a large angle range.
Preferably, the propellant charge is situated outside of the chamber, whereby additionally there is a shared outflow chamber for pressurized gas and combustion products in which chamber they are mixed with each other. This outflow chamber can have a small volume.
The pressure fluid is preferably pressurized gas and the gas generator according to the invention preferably does not have a filter.
The nozzle wall is formed by a disk-shaped insert that is manufactured separately and that forms the front wall of a combustion chamber wall.